1. Field of the Invention
The present invention relates to a method of driving a plasma display panel, the method comprising the steps of:
receiving a series of consecutive original images; and
distributing information from each original image over a first plurality of sub-fields.
The invention also relates to a device for driving a plasma panel display and to a display apparatus.
2. Description of the Related Art
Plasma display panels (PDPS) are widely used for flat TV screens. These panels are simple to form a large unit, emit light by themselves, provide high display quality and achieve high response speed. In order to display an image on such a display unit, the so-called “sub-field driven method” is used. One image frame is shown in a number of successive periods called sub-fields. During a sub-field, an amount of light is emitted which is dependent on the weight of the sub-field. Each sub-field has a different weight. A desired intensity level for a pixel in the image is realized by controlling the specific sub-fields. The human eye sees the sum of the intensity levels of the enabled sub-fields within a field (i.e., an image) due to the integrating character of the human eye. In this way, a sub-field driven method using 8 sub-fields can display a maximum of 28 halftone levels.
Plasma display panels suffer from several motion artifacts. One type of these motion artifacts is Dynamic False Contouring (DFC). DFC may occur in relatively large areas with little luminance differentiation. The DFC artifacts can sufficiently be reduced by using an adapted sub-field distribution. The remaining motion artifacts, such as double/colored edges and motion blur, are caused by the large time difference between the first and last sub-fields of a TV field period. To avoid these artifacts, a sub-field distribution is usually selected showing one central peak. The sub-fields with the highest values are placed in the middle of the frame. Another variant is placing the sub-fields in increasing order so that the sub-fields form a kind of staircase. The staircase variant is used in the CLEAR method, see “Development of new driving method for AC-PDPS: High-Contrast, Low Energy Address and Reduction of False Contour Sequence CLEAR”, by T. Tokunaga et al., Proceedings of the IDW '99, page 787. An example of a distribution using the CLEAR method is shown in FIG. 1a. In FIG. 1a, a histogram is shown which represents the distribution of the sub-fields within one frame period. The first (white) bar represents a set-up of all plasma cells. After the setup phase, all cells are active. The other bars represent the luminance of a plasma cell during the consecutive sub-fields (SF1-SF8). During the first sub-field (SF1), the activated cells will have the lowest luminance (L1). After each sub-field, plasma cells that should be inactive are turned off, and the other cells will remain active. Each cell can be turned off only once per frame period. This means that each extra luminance level is created by using one extra sub-field. All cells are activated once during the set-up phase at the beginning of the frame period.
If the CLEAR method sub-field distribution is used at a 50 Hz frame rate, large area flicker will be visible. “Reduction of large area flicker in plasma display panels”, by B. Salters et al., Proceedings of the SID 2001, page 1098, 2001, San Jose, and “A 50 Hz flicker reduction for PDP and evaluation system development”, by H. Kuriyama et al, Proceedings of the SID 2001, page 1102, 2001, San Jose, disclose that this large area flicker can be reduced by using a sub-field distribution with two peaks. However, such a sub-field distribution will cause more motion artifacts, such as double/colored edges or motion blur.
Another sub-field distribution with an inherent reduction of the dynamic false contour is called LSC (Limited Sub-field Coding). This scheme is described in a U.S. Patent Application Ser. No. 10/082,005, filed Feb. 21, 2002 [PHNL010114EPP] assigned to the Assignee of the present application, entitled “METHOD AND UNIT FOR DISPLAYING AN IMAGE IN SUB-FIELDS”. The idea is that for each increasing gray level, only a limited number of sub-fields change value, which will result in a reduction of the DFC motion artifacts.
In cathode ray tube (CRT) screens, large area flicker and motion artifacts are a well-known problem too. These artifacts are minimized by a concept called motion-compensated up-conversion, also known as Natural Motion, see “Video Processing for multimedia systems”, by G. de Haan, University Press Eindhoven, ISBN 90-9014015-8. An extra image is inserted between two consecutive original images. In this way, the display frequency is doubled from, for example, 50 Hz to 100 Hz. The inserted images are corrected for motion, if motion is present in the video sequence.
Motion compensation is also used in plasma display panels. In “Motion Compensation in Plasma Displays”, by R. van Dijk and T. Holtslag, Proceedings of the IDW 1998, page 543, motion vectors from a video sequence are used to reduce motion artifacts. Basically, all sub-fields are shifted on the motion vectors to make sure that the human eye will integrate all sub-fields in a correct way. This algorithm can give very good moving picture quality, but its implementation is very complex.